Tricalcium phosphate and alumixijm



Reissued 'Aug. 1, 1933 v j Re.' 18,907

U T DIZ'S AT S O ICE rarcALcmM PHOSPHATE, ANn'A UMnto g PHOSPHATE COMPOSITION SALT, William' George Warning 'andTheodoreWiHiam I Schilb, St." Louis, Mo., assignors to Swami Research, Inc.,- a Corporation of Alabama No-Drawing. Original No. 1,865,733, dated July 5, 1932,Serial No. 390,208 September 3, 1 929. Application for 'rcissue Apr-i115, 1933. Serial No. ,322 r 1 10Claims. (Cl. 2 3-1243.)

This invention relates to tri-calciumphosphate and moreparticularly to an improved ,tri-calcium phosphate-more suitable as a filler for preventing caking in salt and similar substances than the tri-calcium phosphate heretofore manufactured.

, In the preparation ofcommon salt for table use and for use in self rising flour it is the usual practice to introduce a filler to reduce thetendency of'the salt to cake. Caking is very objectionable in a product'intended for these purposes. The fillerswhich have found extensive useai'e:- sodium bicarbonate; magnesium carbonate,v dicalcium phosphate and tri-calcium phosphate.

From 0.5%, to 1.5% of these substances are incorporated in fine salt producing a product which 'is relatively freeflowing and subject to storage without caking as compared with the untreated salt. Magnesium carbonate and tri-calcium phosphate are more generally used. These substances may also be applied to other crystalline or granular products where a reduction in a tendency to cake is desired.

This invention has as an object a new composition of matter superior in caking inhibiting properties to those now in common use. A further object is an improvement in tri-calcium phosphate which renders it morev effective in inhibiting caking in crystalline or granular substances.-

These objects are accomplished by the follow. ing invention which sets forth a composition of matter consisting of tri-calcium phosphate and aluminum phosphate. It is common knowledge that when milk of lime is precipitated with phosphoric acid the precipitate is more basicthan normal tri-calcium phosphate (3CaO.P2Os). 'A compound corresponding to the formula has been shown to exist and even more basic compositions may be indicated by analysis on account of adsorbed lime. In the description of this invention, therefore, we do not intend to limit ourselves by the use of theterm tri-calcium phosphate'to the definite compound 3CaO.P2Os

but desire it to be understood that this term is used to include phosphates of lime having a molecular ratio of 3 or more molecules of CaO to one molecule of P205.

We have found that for inhibiting caking in salt, tri-calcium phosphate may be materially improved if it contains 4% to 20% aluminum phosphate (AIPO4), a preferred amount being 7%. The aluminum phosphate may be incorporated in the tri-calcium phosphate in any convenient A1PO4 manner which may readily suggest itself to those versed in the art of chemical manufacture.

, As an illustration of how tri-calcium phosphate containing an effective quantity of. aluminum phosphate maybe advantageously produced, we described in detail the following procedure:

We take 405' pounds of phosphorus pentoxide (P205) as phosphoric acid diluted-tom? Baum. 16 pounds granular metallic aluminum or 47 lbs. purified bauxite are dissolved in aportionof this acid, equivalent to 168 pounds P20 The resulting acid solution of aluminumphospliate (AlPO4) is filteredflfree of insoluble materialand withthe remainder of the original batch of acid.

'The combined acid mixture is fed with agitation into a milk of lime containln'g'437 pounds calcium oxide (Ca O) at a concentration of approximately 105 grams CaO per literr The addition ofthe acid mixture is continued until a 10cc. sample of the slurry requires 2 cc. of 0.1 N alkali to bring to alkaline penolphthale'in end point. Stirring is continued two hours to complete the reaction and .then the slurry may be filtered and dried in the Per cent CaO L. 44.4 P205 Q. 38.1

We have found that other metallic phosphates such as iron may also be used to enhance the oaking inhibiting properties of tri-calcium phosphate but due to the fact that they impart objectionable colors to the finished product they are undesirable scribe the following test:Weincorporated by mechanical mixing-1% of each the caking inv hibiting' substances salt and expose the pared samples in shallow dishes to the. atmosphere preabove a saturated salt (NaCl) solution at 100. F.

' for 2 hours and then removed the samples "and dried them in an oven at 100" F. for 30minutes.

The comparative degree. of caking'in the samples of salt was determined and it was found that specially prepared tri-calcium phosphate containtaining 7% aluminum phosphate first as the quantities'usuallypresent (0.2% to 2.0%' Iare;

not sufiicient to accomplish the improvement caking inhibiting properties gained by our inven aicaking inhibitor with magnesium carbonate second, ordinary'tri-calcium phosphate third, sodium bicarbonate fourth andrdi-calciumgphosphatefifth. v

' It is known that aluminum phosphate pres-v ent to a-limited extent intri-c'aloium'phosphate as ordinarily manufactured ibeing' included unavoidable impurity in the phosphoric acid but tionl' V I Having described thefproperties of jour'i nvention,its application, andfa convenient'method of manufacture, what we claimas newand novel is": 15A dry salt' containiiig' a filler, consisting of tri-calcium phosphate with aluminum phosphate w in'excess Of 1% of the salt.

mately 1% oi a"filler consisting of tri-calcium' phosphate 1 to 20 aluminum phosphate.

3. Dry sodium chloride containing substantially 1% 'joi a caking inhibitor consisting "essentially "of' tri calcium phosphate, containing approximately 7% aluminum phosphate.

:4. Dry sodium "chloride containing 'sufficient :caking'inhibitor to prevent caking said inhibitor 7 I consisting of finely ground tri-calcium phosphate with aluminum phosphate inexcess of 4%.

5. A dry salt containing sufilcient filler to preventcaking, said flller co'nsisting oI-finely ground ftri-calcium phosphate with 4% to 2 0 aluminum phosphate.

6.-A' dry salt containing sufiicient caking in- -hibitor to prevent caking, said inhibitor consisting 1. of Y finely ground tri-calcium taining' 7% aluminum phosphate.

7, A dry or granular substance havphosphate coning'a tendency to;cake in storageand containing 5 being from five to twenty-five times that of aluminum phosphate.

8. A crystalline to cake-in storage and containing a 'filler comprising tri-calcium phosphate with from 4% to 20% of alumihum phosphate, the amount 'or said 'filler'being sumcient to prevent making and not in excessof 1% of 'thesubstan'ce.

stance;

by itself tends to cake in storage',' and containing substance having a tendency sufiicient. filler to prevent caking,' said filler com prising tri-calcium phosphate and aluminum 1 phosphate',"the' amount of tri-calcium phosphate 9. A granular substance; which by itself tends to "cake in storage and'containing a caking in-' hibitor comprising tri-calcium phosphate with from 4 to 20% of aluminum phosphate,"'the amountof said inhibitorbeingsumcient to prevent caking and not in'eircess of- ,1 of the sub- I ;10.vA' crystalline or granular substance which 05 sufficient filler to prevent'caking; said filler com prising *tri-calcium phosphate with approximately 7% of aluminum phosphate incorporated'thereiri.

' GEORGE'WARNINGQ *THEODOBE WI LIAM scams. 

